Todos for 1.5 or further.

- implement "persistent" retrieving.
- allow time-stamping by arbitrary date.
- fix Unix directory parsing to allow for spaces in file names.
- allow size limit to files.
- allow wildcards in -X/-I.
- -k to convert convert relative references to absolute if not downloaded.
- recognize HTML comments.
- download to .in* when mirroring.
- move/delete nonexistent files when mirroring.
- implement a switch to avoid downloading multiple files (e.g. x and x.gz).
- implement uploading (--put local-file?) in FTP and HTTP.
- implement better spider options.
